Wireless communication system, access point, terminal, and communication method

ABSTRACT

A wireless communication system according to the present disclosure includes an access point (AP) belonging to a certain BSS and a terminal (STA) belonging to the AP. The STA updates an NAV used for virtual carrier sense according to whether the AP and the STA are permitted to use OBSS_PD-based SR.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system, anaccess point, a terminal, and a communication method.

BACKGROUND ART

In wireless Local Area Network (LAN) standards Institute of Electricaland Electronics Engineers (IEEE) 802.11, a task group TGax has beenstudying a next-generation communication system IEEE 802.11ax (HEW: HighEfficiency Wireless LAN (WLAN)). Regarding component technologies, it isexpected that IEEE 802.11ax will employ a new modulation/demodulationsystem (1024 Quadrature Amplitude Modulation (QAM)), support uplinkMulti User Multi-Input Multi-Output (MU-MIMO), introduce OrthogonalFrequency-Division Multiple Access (OFDMA), and so on.

Incidentally, with respect to a predetermined Basic Service Set (BSS),another BSS of which the area overlaps with the area of thepredetermined BSS and which uses the same frequency as that of thepredetermined BSS is referred to as an Overlapping BSS (OBSS). Further,a state where a plurality of BSSs coexist as OBSSs with respect to eachother is referred to as an OBSS problem (or an OBSS environment). TheOBSS problem frequently occurs in a Dense deployment environment havinga high deployment density of access points. Further, the Densedeployment environment greatly reduces throughputs of both a terminaland an access point due to interference of the OBSS.

FIG. 1 shows a configuration example of a wireless communication systemin which the OBSS problem is occurring. The area of a BSS 1 overlapswith the area of a BSS 2 and the BSS1 uses the same frequency as that ofthe BSS 2. Accordingly, the BSS 2 is an OBSS with respect to the BSS 1,while the BSS 1 is an OBSS with respect to the BSS 2.

The nodes belonging to the BSS 1 include an access point AP1 forming theBSS 1 and terminals STA1-1 and STA1-2 associated with the access pointAP1. The terminal STA1-1 is located in the area where the BSS 1 and theBSS 2 overlap. This causes communication between the access point AP1and the terminal STA1-1 to receive interference from the BSS 2, therebyreducing throughputs of the access point AP1 and the terminal STA1-1.

The nodes belonging to the BSS 2 include an access point AP2 forming theBSS 2 and terminals STA2-1 and STA2-2 associated with the access pointAP2. The terminal STA2-1 is located in the area where the BSS 1 and theBSS 2 overlap. This causes communication between the access point AP2and the terminal STA2-1 to receive interference from the BSS 1, therebyreducing throughputs of the access point AP2 and the terminal STA2-1.

Note that the above configuration is not limited to being aconfiguration in which two terminals STA1-1 and STA1-2 belong to the BSS1, and it is only required that at least one terminal belong thereto.Hereinafter, a terminal belonging to the BSS 1 is referred to as aterminal STA1 when it is not necessary to specify a terminal. Further,the above configuration is not limited to being a configuration in whichtwo terminals STA2-1 and STA2-2 belong to the BSS 2, and it is onlyrequired that at least one terminal belong thereto. Hereinafter, aterminal belonging to the BSS 2 is referred to as a terminal STA2 whenit is not necessary to specify a terminal. Further, hereinafter, when itis not specified whether a terminal is a terminal STA1 or a terminalSTA2, it is referred to as a terminal STA, and when it is not specifiedwhether an access point is an access point AP1 or an access point AP2,it is referred to as an access point AP.

It is expected that IEEE 802.11ax (HEW) will add a function of SpatialReuse (SR; reuse of space/reuse of frequency) to improve throughput ofthe access point AP in the Dense deployment environment. Two mechanismsof OBSS_Power Detect (PD)-based SR and Two Network Allocation Vectors(NAVs) related to SR are described hereinafter.

First, the OBSS_PD-based SR is described.

The OBSS_PD-based SR has a function in which the access point AP and theterminal STA perform adjustment so as to avoid interference between theBSS and the OBSS by dynamically adjusting transmission power (TXPWR) anda Clear Channel Assessment (CCA) sensitivity level (e.g., see Non-PatentLiterature 1). This function contributes to solving the OBSS problem.However, a specific algorithm for determining the TXPWR and the CCAsensitivity level is implementation-dependent.

Next, the Two NAVs are described.

IEEE 802.11ax (HEW) introduces a mechanism in which the terminal STAdetermines whether the radio frame (e.g., a Physical Layer ConvergenceProtocol (PLCP) Protocol Data Unit (PPDU) frame) received on the channelis a radio frame (an Intra-BSS frame) received from the BSS to which itbelongs or a radio frame (an Inter-BSS frame) received from the OBSS.This determination is made, for example, by checking a BSS color bit andMedia Access Control (MAC) header of the received radio frame (e.g., seeNon-Patent Literature 1). For example, in the example of FIG. 1, theterminal STA1-1 belonging to the BSS 1 determines that the radio framereceived from the access point AP1 or the terminal STA1-2 that belongsto the same BSS 1 is an intra-BSS frame and that the radio framereceived from the access point AP2 or the terminals STA2-1 and STA2-2that belong to the BSS 2 serving as the OBSS is an Inter-BSS frame.

Further, IEEE 802.11ax (HEW) expands a Virtual Carrier Sense functionusing in IEEE 802.11. An existing NAV used in the virtual carrier senseof Distributed Coordination Function (DCF) communication is referred toas a Conventional NAV. The Conventional NAV is the one for setting atransmission prohibition period to the terminal STA by signaling. Duringa period in which the Conventional NAV>0, the terminal STA determines,without performing physical carrier sense, the medium in use to be BUSY(virtual carrier sense) and does not transmit any radio frame. Thus, theConventional NAV contributes to reducing power of the terminal STA andimproving communication efficiency (i.e., contributes to overcoming theso-called hidden terminal problem).

IEEE 802.11ax (HEW) defines new Two NAVs referred to as an Intra-BSS NAVand a Basic NAV in addition to the Conventional NAV (e.g., seeNon-Patent Literature 1).

The Intra-BSS NAV is updated based on a NAV value included in thereceived Intra-BSS frame.

When a reception level of the received radio frame exceeds a thresholdOBSS_PD and the received radio frame is determined to be an Inter-BSSframe, or when the received radio frame cannot be determined to be anIntra-BSS frame, the Basic NAV is updated based on a NAV value includedin the received radio frame. Note that the OBSS_PD is a threshold whichvaries in accordance with transmission power TXPWR (e.g., see Non-PatentLiterature 2).

During a period in which the Intra-BSS NAV>0 or the Basic NAV>0, theterminal STA compatible with IEEE 802.11ax determines, withoutperforming the physical carrier sense, the medium to be BUSY and doesnot transmit any radio frame (virtual carrier sense).

By the above-described operations of the Two NAVs, the terminal STAcompatible with IEEE 802.11ax does not consider the medium in use to beBUSY when a reception level of the Inter-BSS frame received from theOBSS is the threshold OBSS_PD or less. This enables the terminal STAcompatible with IEEE 802.11ax to continue Intra-BSS communication withinthe BSS to which it belongs, thereby preventing a decrease in throughputin the OBSS environment.

CITATION LIST Non-Patent Literature

Non-Patent Literature 1: IEEE 802.11-15/0132r17Non-Patent Literature 2: IEEE 802.11-16/0414r1

SUMMARY OF INVENTION Technical Problem

Incidentally, the setting of the OBSS_PD-based SR depends on theimplementation by the manufacturer of the terminal STA and the accesspoint AP. Accordingly, in some cases, the OBSS_PD-based SR and the TwoNAVs may be used in combination. However, using the OBSS_PD-based SR andthe Two NAVs in combination causes a problem that a behavior of theentire wireless communication system becomes very complicated.

It is therefore one of the objects of the present disclosure to providea wireless communication system, an access point, a terminal and acommunication method capable of solving the above-described problem andpreventing a behavior of an entire wireless communication system frombeing very complicated.

Solution to Problem

In one aspect, a wireless communication system including an access point(AP) that belongs to a certain Basic Service Set (BSS) and a terminal(STA) that belongs to the AP, in which

the STA updates a Network Allocation Vector (NAV) used for virtualcarrier sense according to whether the AP and the STA are permitted touse Overlapping BSS (OBSS)_Power Detect (PD)-based Spatial Reuse (SR)that includes a function of performing adjustment so as to avoidinterference between the BSS and the OBSS.

In one aspect, an access point is an access point (AP) in a wirelesscommunication system, the wireless communication system including the APthat belongs to a certain Basic Service Set (BSS) and a terminal (STA)that belongs to the AP,

the AP including:

a memory configured to store instructions; and

at least one processor configured to process the instructions, in which

the processor instructs the STA to update a Network Allocation Vector(NAV) used for virtual carrier sense according to whether the AP and theSTA are permitted to use Overlapping BSS (OBSS)_Power Detect (PD)-basedSpatial Reuse (SR) that includes a function of performing adjustment soas to avoid interference between the BSS and the OBSS.

In one aspect, a terminal is a terminal (STA) in a wirelesscommunication system, the wireless communication system including anaccess point (AP) that belongs to a certain Basic Service Set (BSS) andthe STA that belongs to the AP,

the STA including:

a memory configured to store instructions; and

at least one processor configured to process the instructions, in which

the processer updates a Network Allocation Vector (NAV) used for virtualcarrier sense according to whether the AP and the STA are permitted touse Overlapping BSS (OBSS)_Power Detect (PD)-based Spatial Reuse (SR)that includes a function of performing adjustment so as to avoidinterference between the BSS and the OBSS.

In one aspect, a communication method is a communication methodperformed by an access point (AP) in a wireless communication system,the wireless communication system including the AP that belongs to acertain Basic Service Set (BSS) and a terminal (STA) that belongs to theAP,

the communication method including instructing the STA to update aNetwork Allocation Vector (NAV) used for virtual carrier sense accordingto whether the AP and the STA are permitted to use Overlapping BSS(OBSS)_Power Detect (PD)-based Spatial Reuse (SR) that includes afunction of performing adjustment so as to avoid interference betweenthe BSS and the OBSS.

In another aspect, a communication method is a communication methodperformed by a terminal (STA) in a wireless communication system, thewireless communication system including an access point (AP) thatbelongs to a certain Basic Service Set (BSS) and the STA that belongs tothe AP,

the communication method including updating a Network Allocation Vector(NAV) used for virtual carrier sense according to whether the AP and theSTA are permitted to use Overlapping BSS (OBSS)_Power Detect (PD)-basedSpatial Reuse (SR) that includes a function of performing adjustment soas to avoid interference between the BSS and the OBSS.

Advantageous Effects of Invention

The above-described aspects can achieve an effect of preventing abehavior of an entire wireless communication system from being verycomplicated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a configuration example of a wireless communication systemin which an OBSS problem is occurring;

FIG. 2 is a sequence diagram for explaining a mode 1 in a wirelesscommunication system according to a first example embodiment;

FIG. 3 is a sequence diagram for explaining a mode 2 in the wirelesscommunication system according to the first example embodiment;

FIG. 4 is a sequence diagram for explaining a mode 3 in the wirelesscommunication system according to the first example embodiment;

FIG. 5 is a sequence diagram for explaining a mode 4 in the wirelesscommunication system according to a second example embodiment;

FIG. 6 is a sequence diagram for explaining an operation example 1 inthe wireless communication system according to a third exampleembodiment;

FIG. 7 is a sequence diagram for explaining an operation example 2 inthe wireless communication system according to the third exampleembodiment;

FIG. 8 is a sequence diagram for explaining an operation example 3 inthe wireless communication system according to the third exampleembodiment;

FIG. 9 is a block diagram showing a configuration example of an accesspoint in a certain aspect; and

FIG. 10 is a block diagram showing a configuration example of a terminalin a certain aspect.

DESCRIPTION OF EMBODIMENTS

Example embodiments of the present disclosure will be describedhereinafter with reference to the drawings. A configuration of awireless communication system according to each example embodimentdescribed below is the same as the one shown in FIG. 1, and includesaccess points AP and terminals STA.

The terminals STA are roughly classified as being either a terminal STAcompatible with IEEE 802.11ax or a terminal STA incompatible with IEEE802.11ax.

The terminal STA compatible with IEEE 802.11ax holds three NAVs insidethereof, which are a Conventional NAV and Two NAVs (an Intra-BSS NAV anda Basic NAV), and uses at least one of the three NAVs to perform thevirtual carrier sense. Note that the terminal STA compatible IEEE802.11ax may handle the Conventional NAV and the Basic NAV in a unifiedmanner. In such a case, the terminal STA compatible with IEEE 802.11axholds the Basic NAV (this Basic NAV is equated with the ConventionalNAV) and the Intra-BSS NAV inside thereof. Further, the OBSS_PD-based SRcan be set to the terminal STA compatible with IEEE 802.11ax.

On the other hand, the terminal STA incompatible with IEEE 802.11axholds only the Conventional NAV inside thereof and performs the virtualcarrier sense using the Conventional NAV. Further, the OBSS_PD-based SRcannot be set to the terminal STA incompatible with IEEE 802.11ax.

(1) First Example Embodiment

IEEE 802.11ax (HEW) adds two mechanisms which are the OBSS_PD-based SRand the Two NAVs. In a wireless communication system, however, using theOBSS_PD-based SR and the Two NAVs in combination causes a problem that abehavior of the entire wireless communication system becomes verycomplicated.

In the first example embodiment, therefore, in a predetermined BSS, theNAV which the terminal STA compatible with IEEE 802.11ax uses for thevirtual carrier sense is adaptively switched according to whethersettings of the OBSS_PD-based SR in the access point AP and the terminalSTA compatible with IEEE 802.11ax that belong to that BSS is set to on(in other words, whether the OBSS_PD-based SR is enabled. The sameapplies hereinafter.).

Specifically, the wireless communication system according to the firstexample embodiment includes modes 0, 1, 2, and 3 as operation modes ofthe virtual carrier sense, and switches the NAV which the terminal STAcompatible with IEEE 802.11ax uses for the virtual carrier sense byswitching between the modes 0, 1, 2, and 3. The modes 0, 1, 2, and 3 aredescribed hereinafter. In the modes 0, 1, 2, and 3, as terminals STAsbelonging to the BSS, both the terminal STA compatible with IEEE802.11ax and the terminal STA incompatible with IEEE 802.11ax may bepresent or only the terminals STAs compatible with IEEE 802.11ax may bepresent. Note that an operation in the BSS 1 will be describedhereinafter as an example and the same applies to an operation in theBSS 2.

Mode 0:

A mode 0 is a mode similar to that of related art using OBSS_PD-based SRand two NAVs in combination.

The mode 0 is performed under the environment where settings of theOBSS_PD-based SR in the access point AP1 and the terminal STA1compatible with IEEE 802.11ax that belong to the BSS 1 is set to on.

In the mode 0, the terminal STA1 compatible with IEEE 802.11ax uses theConventional NAV and the two NAVs (the Intra-BSS NAV and the Basic NAV)to perform virtual carrier sense, and the terminal STA1 incompatiblewith IEEE 802.11ax uses the Conventional NAV to perform the virtualcarrier sense.

The following Table 1 shows a summary of the mode 0.

TABLE 1 Terminal STA compatible with IEEE ∘(present) 802.11ax TerminalSTA incompatible with IEEE ∘(present) or x(not present) 802.11axOBSS_PD-based SR ∘(set) Conventional NAV ∘(used) Intra-BSS NAV ∘(used)Basic NAV ∘(used)

Mode 1:

A mode 1 is performed under the environment where settings of theOBSS_PD-based SR in the access point AP1 and the terminal STA1compatible with IEEE 802.11ax that belong to the BSS 1 is set to on.

In the mode 1, the terminal STA1 compatible with IEEE 802.11ax and theterminal STA1 incompatible with IEEE 802.11ax both use only theConventional NAV to perform the virtual carrier sense.

The following Table 2 shows a summary of the mode 1.

TABLE 2 Terminal STA compatible with IEEE ∘(present) 802.11ax TerminalSTA incompatible with IEEE ∘(present) or x(not present) 802.11axOBSS_PD-based SR ∘(set) Conventional NAV ∘(used) Intra-BSS NAV x(unused)Basic NAV x(unused)

Mode 2:

A mode 2 is performed under the environment where settings of theOBSS_PD-based SR in the access point AP1 and the terminal STA1compatible with the IEEE 802.11ax that belong to the BSS 1 is set to off(in other words, the OBSS_PD-based SR is prohibited. The same applieshereinafter).

In the mode 2, the terminal STA1 compatible with IEEE 802.11ax and theterminal STA1 incompatible with IEEE 802.11ax both use only theConventional NAV to perform the virtual carrier sense.

The following Table 3 shows a summary of the mode 2.

TABLE 3 Terminal STA compatible with IEEE ∘(present) 802.11ax TerminalSTA incompatible with IEEE ∘(present) or x(not present) 802.11axOBSS_PD-based SR x(not set) Conventional NAV ∘(used) Intra-BSS NAVx(unused) Basic NAV x(unused)

Mode 3:

A mode 3 is performed under the environment where settings of theOBSS_PD-based SR in the access point AP1 and the terminal STA1compatible with the IEEE 802.11ax that belong to the BSS 1 is set tooff.

In the mode 3, the terminal STA1 compatible with IEEE 802.11ax uses theConventional NAV, the Intra-BSS NAV and the Basic NAV to perform thevirtual carrier sense. The terminal STA1 compatible with IEEE 802.11axdetermines, upon receiving a radio frame (e.g., a PPDU frame, a RequestTo Send (RTS)/Clear To send (CTS) frame) including a NAV value, whetherthe received radio frame is an Intra-BSS frame received from the BSS 1to which it belongs or an Inter-BSS frame received from the BSS 2serving as the OBSS. When the terminal STA1 compatible with IEEE802.11ax determines the received radio frame to be an Intra-BSS frame,it updates the Conventional NAV and the Intra-BSS NAV based on the NAVvalue included in the Intra-BSS frame. When the terminal STA1 compatiblewith IEEE 802.11ax determines the received radio frame to be anIntra-BSS, it updates the Conventional NAV and the Basic NAV based onthe NAV value included in the Intra-BSS frame.

On the other hand, the terminal STA1 incompatible with IEEE 802.11axuses only the Conventional NAV to perform the virtual carrier sense.

The following Table 4 shows a summary of the mode 3.

TABLE 4 Terminal STA compatible with IEEE ∘(present) 802.11ax TerminalSTA incompatible with IEEE ∘(present) or x(not present) 802.11axOBSS_PD-based SR x(not set) Conventional NAV ∘(used) Intra-BSS NAV∘(used) Basic NAV ∘(used)

Next, a specific example for achieving the mode 1 is described withreference to FIG. 2.

First, the access point AP1 belonging to the BSS 1 transmits, to all theterminals STA1 compatible with the IEEE 802.11ax belonging to the BSS 1,signaling which instructs them to invalidate the Intra-BSS NAV and theBasic NAV other than the Conventional NAV (Step S101). The access pointAP1 includes this signaling, for example, in a radio frame such as abeacon frame and transmits it.

When the terminal STA1 compatible with IEEE 802.11ax receives thatsignaling from the access point AP1, it invalidates the Intra-BSS NAVand the Basic NAV other than the Conventional NAV. Note that it isassumed that there are two forms of invalidating the NAV: one in whichthe NAV is disabled and another one in which a Special Value such as 0is set (fixed) to the NAV (The same applies hereinafter). Consequently,only the Conventional NAV is validated (Step S102). After that, theterminal STA1 compatible with IEEE 802.11ax therefore uses only theConventional NAV to perform the virtual carrier sense.

When the terminal STA1 compatible with IEEE 802.11ax receives a radioframe such as a PPDU frame and an RTS/CTS frame from the access pointAP1 of the BSS 1 to which it belongs (Step S103), it updates theConventional NAV based on the NAV value included in the received radioframe (Step S104). After that, the terminal STA1 compatible with IEEE802.11ax does not perform the physical carrier sense in a period T1 inwhich the Conventional NAV>0, considers the medium in use to be BUSY(virtual carrier sense), and does not transmit a radio frame.

Further, when the terminal STA1 compatible with IEEE 802.11ax receives aradio frame such as a PPDU frame and an RTS/CTS frame from the accesspoint AP2 which belongs to the BSS 2 serving as the OBSS in the samemedium as the above one (Step S105), it updates the Conventional NAVbased on the NAV value included in the received radio frame (Step S106).

Then, when the Conventional NAV=0, the terminal STA1 compatible withIEEE 802.11ax resumes the physical carrier sense (Step S107).

Note that the terminal STA1 incompatible with IEEE 802.11ax does nothold the Two NAVs and accordingly uses the Conventional NAV to performthe virtual carrier sense. This operation is the same as that of relatedart and the explanation thereof is thus omitted.

Next, a specific example for achieving the mode 2 is described withreference to FIG. 3.

First, the access point AP1 belonging to the BSS 1 transmits, to all theterminals STA1 compatible with the IEEE 802.11ax belonging to the BSS 1,signaling which instructs them to turn off the setting of the OBSS_PDbased SR and to invalidate the Intra-BSS NAV and the Basic NAV otherthan the Conventional NAV (Step S201). The access point AP1 includesthis signaling, for example, in an HE operation element or a capabilityelement of a radio frame such as a beacon frame and transmits it.

When the terminal STA1 compatible with IEEE 802.11ax receives thatsignaling from the access point AP1, it turns off the setting of theOBSS_PD based SR (Step S202). Further, the terminal STA1 compatible withIEEE 802.11ax invalidates the Intra-BSS NAV and the Basic NAV other thanthe Conventional NAV. Consequently, only the Conventional NAV isvalidated (Step S203). After that, the terminal STA1 compatible withIEEE 802.11ax therefore uses only the Conventional NAV to perform thevirtual carrier sense.

When the terminal STA1 compatible with IEEE 802.11ax receives a radioframe such as a PPDU frame and an RTS/CTS frame from the access pointAP1 of the BSS 1 to which it belongs (Step S204), it updates theConventional NAV based on the NAV value included in the received radioframe (Step S205). After that, the terminal STA1 compatible with IEEE802.11ax does not perform physical carrier sense in a period T2 in whichthe Conventional NAV>0, considers the medium in use to be BUSY (virtualcarrier sense), and does not transmit a radio frame.

Further, when the terminal STA1 compatible with IEEE 802.11ax receives aradio frame such as a PPDU frame and an RTS/CTS frame from the accesspoint AP2 which belongs to the BSS 2 serving as the OBSS in the samemedium as the above one (Step S206), it updates the Conventional NAVbased on the NAV value included in the received radio frame (Step S207).

Then, when the Conventional NAV=0, the terminal STA1 compatible withIEEE 802.11ax resumes the physical carrier sense (Step S208).

Note that the terminal STA1 incompatible with IEEE 802.11ax does nothold the Two NAVs and accordingly uses the Conventional NAV to performthe virtual carrier sense. This operation is the same as that of relatedart and the explanation thereof is thus omitted.

Next, a specific example for achieving the mode 3 is described withreference to FIG. 4.

First, the access point AP1 belonging to the BSS 1 transmits, to all theterminals STA1 compatible with the IEEE 802.11ax belonging to the BSS 1,signaling which instructs them to turn off the setting of the OBSS_PDbased SR (Step S301). The access point AP1 includes this signaling, forexample, in an HE operation element or a capability element of a radioframe such as a beacon frame and transmits this.

When the terminal STA1 compatible with IEEE 802.11ax receives thatsignaling from the access point AP1, it turns off the setting of theOBSS_PD based SR (Step S302). Further, the terminal STA1 compatible withIEEE 802.11ax randomly selects an OBSS_PD value for determining whetherthe received radio frame is an Intra-BSS frame or an Inter-BSS frame(Step S303). As for the OBSS_PD value, for example, a default value(e.g., OBSS_PDmin) or OBSS_PDmin notified in advance from the accesspoint AP1 may be selected.

In this case, the Conventional NAV, the Intra-BSS NAV, and the Basic NAVall remain validated. After that, the terminal STA1 compatible with IEEE802.11ax therefore uses the Conventional NAV, the Intra-BSS NAV and theBasic NAV to perform the virtual carrier sense.

When the terminal STA1 compatible with IEEE 802.11ax receives a radioframe such as a PPDU frame and an RTS/CTS frame from the access pointAP1 of the BSS 1 to which it belongs (Step S304), it determines whetherthe received radio frame is an Intra-BSS frame or an Inter-BSS frame,for example, by comparing a reception level of the received radio framewith the OBSS_PD value (Step S305).

Note that the radio frame received in Step S304 is an Intra-BSS frameand accordingly the terminal STA1 compatible with IEEE 802.11ax updatesthe Conventional NAV and the Intra-BSS NAV based on the NAV valueincluded in the Intra-BSS frame (Steps S306 and S307). On the otherhand, it does not update the Inter-BSS NAV. After that, in a period T3in which one of the Conventional NAV, the Intra-BSS NAV and the BasicNAV indicates a value greater than 0, the terminal STA1 compatible withIEEE 802.11ax does not perform physical carrier sense, considers themedium in use to be BUSY (virtual carrier sense), and does not transmita radio frame.

Further, when the terminal STA1 compatible with IEEE 802.11ax receives aradio frame such as a PPDU frame and an RTS/CTS frame from the accesspoint AP2 which belongs to the BSS 2 serving as the OBSS in the samemedium (Step S308), it determines whether the received radio frame is anIntra-BSS frame or an Inter-BSS frame, for example, by comparing areception level of the received radio frame with the OBSS_PD value (StepS309).

Note that the radio frame received in Step S308 is an Inter-BSS frameand accordingly the terminal STA1 compatible with IEEE 802.11ax updatesthe Conventional NAV and the Basic NAV based on the NAV value includedin the Inter-BSS frame (Steps S310 and S311). On the other hand, it doesnot update the Intra-BSS NAV. Performing the virtual carrier sense iscontinued during a period in which the Conventional NAV or the Basic NAVindicates a value greater than 0 even when the Intra-BSS NAV=0.

Then, when all the Conventional NAV, the Intra-BSS NAV and the Basic NAVare 0, the terminal STA1 compatible with IEEE 802.11ax resumes thephysical carrier sense (Step S312).

According to the first example embodiment, as described above, the NAVwhich the terminal STA compatible with IEEE 802.11ax uses for thevirtual carrier sense is switched according to whether settings of theOBSS_PD-based SR in the access point AP and the terminal STA compatiblewith IEEE 802.11ax that belong to the BSS is set to on.

This reduces the cases in which the OBSS_PD-based SR and the Two NAVsare used in combination and thus makes it possible to prevent a behaviorof the entire wireless communication system from being very complicated.Further, this simplifies the behavior of the entire wirelesscommunication system and thus makes it possible to achieve a stablecommunication state.

For example, under the environment where settings of the OBSS_PD-basedSR in the access point AP1 and the terminal STA1 compatible with IEEE802.11ax that belong to the BSS 1 is set to on, the mode 1 is performed.In the mode 1, the terminal STA1 compatible with IEEE 802.11ax uses onlythe Conventional NAV to perform the virtual carrier sense. Performingthe mode 1 under such the environment prevents the terminal STA1incompatible with IEEE 802.11ax from being at a disadvantage when boththe terminal STA1 compatible with IEEE 802.11ax and the terminal STA1incompatible with IEEE 802.11ax are present as the terminals STA1belonging to the BSS 1. This is described hereinafter.

For example, it is assumed that the terminal STA1 compatible with IEEE802.11ax uses the Basic NAV to perform the virtual carrier sense. Whenthe terminal STA1 incompatible with IEEE 802.11ax receives a radio framefrom the BSS 2 serving as the OBSS, it sets the Conventional NAV andenters a transmission prohibited period to prevent communication. On theother hand, when the terminal STA1 compatible with IEEE 802.11axreceives a radio frame from the BSS 2, there is a possibility that itmay acquire a transmission opportunity (TXOP) without setting the basicNAV by a function of the OBSS_PD value and start communication withinthe BSS 1. In such a case, the radio frame transmitted from the terminalSTA1 compatible with IEEE 802.11ax causes the terminal STA1 incompatiblewith IEEE 802.11ax to set new Conventional NAV, and consequently theterminal STA1 incompatible with IEEE 802.11ax cannot perform theIntra-BSS communication within the BSS 1 even when the interference fromthe BSS 2 is reduced. Therefore, the terminal STA1 incompatible withIEEE 802.11ax may be more disadvantageous than the terminal STA1compatible with IEEE 802.11ax in view of throughput and communicationefficiency. In the mode 1, however, not only the terminal STA1incompatible with IEEE 802.11ax but also the terminal STA1 compatiblewith IEEE 802.11ax uses the Conventional NAV, thereby making it possibleto prevent the terminal STA1 incompatible with IEEE 802.11ax from beingdisadvantageous.

(2) Second Example Embodiment

IEEE 802.11ax (HEW) adds two mechanisms which are the OBSS_PD-based SRand the Two NAVs. In a wireless communication system, however, using theOBSS_PD-based SR and the Two NAVs in combination causes a problem that abehavior of the entire wireless communication system becomes verycomplicated. Further, in a certain BSS, under the special environmentwhere only the terminal STA compatible with IEEE 802.11ax is present asthe terminal STA belonging to that BSS, the OBSS_PD-based SR can be setto all the terminals STA belonging to that BSS. Consequently, if theOBSS_PD-based SR functions appropriately, the number of occasions inwhich frames are received from the terminal STA or the access point APthat belong to the OBSS is reduced and the Intra-BSS communicationwithin the BSS is less likely to interfere with the intra-BSScommunication within the OBSS. The need for having the terminal STA usethe Two NAVs is thus reduced.

In a second example embodiment, therefore, in a predetermined BSS, theNAV which the terminal STA compatible with IEEE 802.11ax uses for thevirtual carrier sense is adaptively switched according to whether onlythe terminal STA compatible with IEEE 802.11ax is present as theterminal STA belonging to that BSS or both the terminal STA compatiblewith IEEE 802.11ax and the terminal STA incompatible with IEEE 802.11axare present as the terminals STA belonging to that BSS under theenvironment where settings of the OBSS_PD-based SR in the access pointAP and the terminal STA compatible with IEEE 802.11ax that belong tothat BSS is set to on.

Specifically, the wireless communication system according to the secondexample embodiment includes modes 0′ and 4 as operation modes of thevirtual carrier sense and switches the NAV which the terminal STAcompatible with IEEE 802.11ax uses for the virtual carrier sense byswitching between the modes 0′ and 4. The modes 0′ and 4 are describedhereinafter. Note that an operation in the BSS 1 will be describedhereinafter as an example and the same applies to an operation in theBSS 2.

Mode 0′:

A mode 0′ is different from the mode 0 only in that it is limited tobeing performed under the environment where only the terminal STA1compatible with IEEE 802.11ax is present as the terminal STA1 belongingto the BSS 1. That is, the mode 0′ is performed under the environmentwhere only the terminal STA1 compatible with IEEE 802.11ax is present asthe terminal STA1 belonging to the BSS 1 and where settings of theOBSS_PD-based SR in the access point AP1 and the terminal STA1compatible with IEEE 802.11ax that belong to the BSS 1 is set to on.

In the mode 0′, the terminal STA1 compatible with IEEE 802.11ax uses theConventional NAV and the two NAVs (the Intra-BSS NAV and the Basic NAV)to perform the virtual carrier sense, and the terminal STA1 incompatiblewith IEEE 802.11ax uses the Conventional NAV to perform the virtualcarrier sense.

The following Table 5 shows a summary of the mode 0′.

TABLE 5 Terminal STA compatible with IEEE 802.11ax ∘(present) TerminalSTA incompatible with IEEE x(not present) 802.11ax OBSS_PD-based SR∘(set) Conventional NAV ∘(used) Intra-BSS NAV ∘(used) Basic NAV ∘(used)

Mode 4:

A mode 4 is performed under the environment where only the terminal STA1compatible with IEEE 802.11ax is present as the terminal STA1 belongingto the BSS 1 and where settings of the OBSS_PD-based SR in the accesspoint AP1 and the terminal STA1 compatible with IEEE 802.11ax thatbelong to the BSS 1 is set to on.

In the mode 4, the terminal STA1 compatible with IEEE 802.11ax uses onlythe Intra-BSS NAV to perform the virtual carrier sense. The terminalSTA1 compatible with IEEE 802.11ax determines, upon receiving a radioframe (e.g., a PPDU frame, an RTS/CTS frame) including a NAV value,whether the received radio frame is an Intra-BSS frame received from theBSS 1 to which it belongs or an Inter-BSS frame received from the BSS 2serving as the OBSS. When the terminal STA1 compatible with IEEE802.11ax determines the received radio frame to be an Intra-BSS frame,it updates the Intra-BSS NAV based on the NAV value included in theIntra-BSS frame.

The following Table 6 shows a summary of the mode 4.

TABLE 6 Terminal STA compatible with IEEE 802.11ax ∘(present) TerminalSTA incompatible with IEEE x(not present) 802.11ax OBSS_PD-based SR∘(set) Conventional NAV x(unused) Intra-BSS NAV ∘(use) Basic NAVx(unused)

Next, a specific example for achieving the mode 4 is described withreference to FIG. 5.

First, the access point AP1 belonging to the BSS 1 transmits, to all theterminals STA1 compatible with the IEEE 802.11ax belonging to the BSS 1,signaling which instructs them to invalidate the Basic NAV and theConventional NAV other than the Intra-BSS NAV (Step S401). The accesspoint AP1 includes this signaling, for example, in a radio frame such asa beacon frame and transmits it.

When the terminal STA1 compatible with IEEE 802.11ax receives thatsignaling from the access point AP1, it invalidates the Basic NAV andthe Conventional NAV other than the Intra-BSS NAV. Consequently, onlythe Intra-BSS NAV is validated (Step S402). After that, the terminalSTA1 compatible with IEEE 802.11ax therefore uses only the Intra-BSS NAVto perform the virtual carrier sense. Further, the terminal STA1compatible with IEEE 802.11ax randomly selects an OBSS_PD value fordetermining whether the received radio frame is an Intra-BSS frame or anInter-BSS frame (Step S403). As for the OBSS_PD value, for example, adefault value (e.g., OBSS_PDmin) or OBSS_PDmin notified in advance fromthe access point AP1 may be selected.

When the terminal STA1 compatible with IEEE 802.11ax receives a radioframe such as a PPDU frame and an RTS/CTS frame from the access pointAP1 of the BSS 1 to which it belongs (Step S404), it determines whetherthe received radio frame is an Intra-BSS frame or an Inter-BSS frame,for example, by comparing a reception level of the received radio framewith the OBSS_PD value (Step S405).

Note that the radio frame received in Step S404 is an Intra-BSS frameand accordingly the terminal STA1 compatible with IEEE 802.11ax updatesthe Intra-BSS NAV based on the NAV value included in the Intra-BSS frame(Step S406). After that, in a period T4 in which the Intra-BSS NAV>0,the terminal STA1 compatible with IEEE 802.11ax does not performphysical carrier sense, considers the medium in use to be BUSY (virtualcarrier sense), and does not transmit a radio frame.

Further, when the access point AP2 and the terminal STA2 compatible withthe IEEE 802.11ax that belong to the BSS 2 serving as the OBSS have theOBSS_PD-based SR function properly, the event in which the terminal STA1compatible with the IEEE 802.11ax receives a radio frame from the BSS 2is less likely to occur. However, it is assumed here that the terminalSTA1 compatible with IEEE 802.11ax accidentally receives a radio framefrom the access point AP2 that belongs to the BSS 2 serving as the OBSSon the same medium as the above one (Step S407). In such a case, theterminal STA1 compatible with IEEE 802.11ax determines whether thereceived radio frame is an Intra-BSS frame or an Inter-BSS frame, forexample, by comparing a reception level of the received radio frame withthe OBSS_PD value (Step S408).

Note that the radio frame received in Step S407 is an Inter-BSS frame.However, the terminal STA1 compatible with IEEE 802.11ax invalidates thebasic NAV and the Conventional NAV and accordingly does not update thevalue. Thus, it does not affect the virtual carrier sense.

Then, when the Intra-BSS NAV=0, the terminal STA1 compatible with IEEE802.11ax resumes the physical carrier sense (Step S409).

According to the second example embodiment, as described above, the NAVwhich the terminal STA incompatible with IEEE 802.11ax uses for thevirtual carrier sense is switched, under the environment where settingsof the OBSS_PD-based SR in the access point AP and the terminal STAcompatible with IEEE 802.11ax that belong to a BSS is set to on,according to whether only the terminal STA compatible with IEEE 802.11axis present as the terminal STA belonging to that BSS or both theterminal STA compatible with IEEE 802.11ax and the terminal STAincompatible with IEEE 802.11ax are present as the terminals STAbelonging to that BSS.

This reduces the cases where the OBSS_PD-based SR and the Two NAVs areused in combination and thus makes it possible to prevent a behavior ofthe entire wireless communication system from being very complicated.Further, this simplifies the behavior of the entire wirelesscommunication system and thus makes it possible to achieve a stablecommunication state.

For example, under the environment where settings of the OBSS_PD-basedSR in the access point AP1 and the terminal STA1 compatible with IEEE802.11ax that belong to the BSS 1 is set to on and where only theterminal STA1 compatible with IEEE 802.11ax is present as the terminalSTA1, the mode 4 is performed. In the mode 4, the terminal STA1compatible with IEEE 802.11ax uses only the Intra-BSS NAV to perform thevirtual carrier sense. The terminal STA1 compatible with IEEE 802.11axdetermines, upon receiving a radio frame including a NAV value, whetherthe received radio frame is an Intra-BSS frame received from the BSS 1to which it belongs or an Inter-BSS frame received from the BSS 2serving as the OBSS, and then updates the Intra-BSS NAV based on the NAVvalue included in the Intra-BSS frame only when determining the receivedradio frame to be the Intra-BSS frame.

If the terminal STA1 compatible with IEEE 802.11ax uses the Two NAVsunder the environment where only the terminal STA1 compatible with IEEE802.11ax is present as the terminal STA1 belonging to the BSS 1, thereis a possibility that it may accidentally receive the NAV at a strongreception level from the BSS 2 serving as the OBSS and set the BasicNAV. However, when the OBSS_PD-based SR functions properly, theIntra-BSS communication within the BSS 2 performed during thetransmission prohibited period set by that Basic NAV does not interferewith the Intra-BSS communication within the BSS 1. Consequently, whenthe Basic NAV prevents the Intra-BSS communication within the BSS 1performed by the terminal STA1, the case where throughput andcommunication efficiency of the terminal STA1 deteriorate may occur. Inthe mode 4, the terminal STA1 compatible with IEEE 802.11ax does not usethe Basic NAV and thus such a case can be prevented from occurring.

(3) Third Example Embodiment

IEEE 802.11ax (HEW) adds two mechanisms which are the OBSS_PD-based SRand the Two NAVs. In a wireless communication system, however, thesetting of the OBSS_PD-based SR in the access point AP and the terminalSTA compatible with IEEE 802.11ax is implementation-dependent. Thiscauses a problem that a behavior of the entire wireless communicationsystem cannot be predicted.

Hence, in a third example embodiment, the setting of the OBSS_PD-basedSR in the access point AP and the terminal STA compatible with IEEE802.11ax is adaptively turned on/off. Three operation examples in thethird example embodiment are described hereinafter. Note that operationsin the BSS 1 will be described hereinafter as examples and the sameapplies to operations in the BSS 2.

Operation Example 1

First, an operation example 1 is described with reference to FIG. 6. Theaccess point AP1 belonging to the BSS 1 recognizes the number of theterminals STA1 incompatible with the IEEE 802.11ax belonging to the BSS1. It is assumed here that the access point AP1 has determined that thenumber of the terminals STA1 incompatible with IEEE 802.11ax has becomeequal to or greater than a predetermined threshold (Step S501).

Then, the access point AP1 turns off the setting of its ownOBSS_PD-based SR (Step S502). Further, the access point AP1 transmits,to all the terminals STA1 compatible with IEEE 802.11ax belonging to theBSS 1, signaling which instructs them to turn off the setting of theOBSS_PD-based SR (Step S503). The access point AP1 includes thissignaling, for example, in an HE operation element or a capabilityelement of a radio frame such as a beacon frame and transmits it.

The terminal STA1 compatible with IEEE 802.11ax turns off the setting ofits own OBSS_PD-based SR upon receiving the aforementioned signalingfrom the access point AP1 (Step S504).

Note that this operation example 1 may add the following operations whenthe number of the terminals STA1 incompatible with the IEEE 802.11axbelonging to the BSS 1 becomes equal to or greater than a predeterminedthreshold.

In Step S503, the access point AP1 transmits signaling which instructsthe terminals to turn off the setting of the Two NAVs (in other words,to have the Two NAVs disabled. The same applies hereinafter.).

In Step S504, the terminal STA1 compatible with IEEE 802.11ax turns offthe setting of its own Two NAVs.

The signaling in Step S503 may be a signal indicating, for example, thata BSS color bit is invalidated.

Operation Example 2

Next, an operation example 2 is described with reference to FIG. 7. Theexplanation will be given assuming here that the only terminals STA1belonging to the BSS 1 are the terminals STA1-1 and STA1-2 compatiblewith IEEE 802.11ax (see FIG. 1).

It is assumed that the terminal STA1-1 compatible with the IEEE 802.11axbelonging to the BSS 1 has detected a beacon frame or the liketransmitted from the access point AP2 belonging to the BSS 2 whichserves as the OBSS (Step S601). Further, it is assumed that the beaconframe or the like has included an instruction to turn off the setting ofthe OBSS_PD-based SR.

Then, similarly, the terminal STA1-1 compatible with the IEEE 802.11axturns off the setting of its own OBSS_PD-based SR (Step S602). Further,the terminal STA1-1 compatible with IEEE 802.11ax transmits, to theaccess point AP1 belonging to the BSS 1, signaling (first signaling)which notifies the access point AP1 of the setting of its ownOBSS_PD-based SR (Step S603). The terminal STA1-1 compatible with IEEE802.11ax includes this signaling, for example, in an HE operationelement or a capability element of the radio frame such as a managementframe and transmits it.

The access point AP1 turns off the setting of its own OBSS_PD-based SRin the same manner as that of the terminal STA1-1 compatible with IEEE802.11ax upon receiving the aforementioned signaling from the terminalSTA1-1 (Step S604). Further, the access point AP1 transmits, to all theterminals STA1-1 and STA1-2 compatible with IEEE 802.11ax belonging tothe BSS 1, signaling (second signaling) which instructs them to turn offthe setting of the OBSS_PD-based SR in the same manner as that of theterminal STA1-1 (Step S605). The access point AP1 includes thissignaling, for example, in an HE operation element or a capabilityelement of the radio frame such as a beacon frame and transmits it.

The terminal STA1-2 compatible with IEEE 802.11ax turns off the settingof its own OBSS_PD-based SR in the same manner as that of the terminalSTA1-1 upon receiving the aforementioned signaling from the access pointAP1 (Step S606). Note that the terminal STA1-1 compatible with the IEEE802.11ax has already turned off its own setting of the OBSS_PD-based SRat the time of Step S602 and maintains this setting.

Note that this operation example 2 may add the following operations whenthe beacon frame or the like, which the terminal STA1-1 compatible withthe IEEE 802.11ax has received from the access point AP2, includes aninstruction to turn off (invalidate) the setting of the Two NAVs (theIntra-BSS NAV and the Basic NAV).

In Step S602, the terminal STA1-1 compatible with the IEEE 802.11axturns off the setting of its own Two NAVs.

In Step S603, the terminal STA1-1 compatible with the IEEE 802.11axtransmits signaling which notifies the access point AP1 of the settingof its own Two NAVs.

In Step S605, the access point AP1 transmits signaling which instructsthe terminals to turn off the setting of the Two NAVs.

In Step S606, the terminal STA1-2 compatible with the IEEE 802.11axturns off the setting of its own Two NAVs.

Further, on the contrary, this operation example 2 may add the followingoperations when the beacon frame or the like, which the terminal STA1-1compatible with the IEEE 802.11ax has received from the access pointAP2, includes an instruction to turn on the setting of the Two NAVs (theIntra-BSS NAV and the Basic NAV) (in other words, the Two NAVs areenabled. The same applies hereinafter.).

In Step S602, the terminal STA1-1 compatible with the IEEE 802.11axturns on the setting of its own Two NAVs.

In Step S603, the terminal STA1-1 compatible with the IEEE 802.11axtransmits signaling which notifies the access point AP1 of the settingof its own Two NAVs.

In Step S605, the access point AP1 transmits signaling which instructsthe terminals to turn on the setting of the Two NAVs.

In Step S606, the terminal STA1-2 compatible with the IEEE 802.11axturns on the setting of its own Two NAVs.

Operation Example 3

Next, an operation example 3 is described with reference to FIG. 8. Theexplanation will be given assuming here that the only terminals STA1belonging to the BSS 1 are the terminals STA1-1 and STA1-2 compatiblewith IEEE 802.11ax (see FIG. 1).

It is assumed that the terminal STA1-1 compatible with the IEEE 802.11axbelonging to the BSS 1 has detected a PPDU frame or the like transmittedfrom the access point AP2 belonging to the BSS 2 which serves as theOBSS (Step S701).

Then, the terminal STA1-1 compatible with the IEEE 802.11ax turns on thesetting of its own OBSS_PD-based SR (Step S702). Further, the terminalSTA1-1 compatible with IEEE 802.11ax transmits, to the access point AP1belonging to the BSS 1, signaling (first signaling) which notifies theaccess point AP1 of the setting of its own OBSS_PD-based SR (Step S703).The terminal STA1-1 compatible with IEEE 802.11ax includes thissignaling, for example, in an HE operation element or a capabilityelement of a radio frame such as a management frame and transmits it.

The access point AP1 turns on the setting of its own OBSS_PD-based SR inthe same manner as that of the terminal STA1-1 compatible with IEEE802.11ax upon receiving the aforementioned signaling from the terminalSTA1-1 (Step S704). Further, the access point AP1 transmits, to all theterminals STA1-1 and STA1-2 compatible with IEEE 802.11ax belonging tothe BSS 1, signaling (second signaling) which instructs them to turn onthe setting of the OBSS_PD-based SR in the same manner as that of theterminal STA1-1 (Step S705). The access point AP1 includes thissignaling, for example, in an HE operation element or a capabilityelement of a radio frame such as a beacon frame and transmits it.

The terminal STA1-2 compatible with IEEE 802.11ax turns on the settingof its own OBSS_PD-based SR in the same manner as that of the terminalSTA1-1 upon receiving the aforementioned signaling from the access pointAP1 (Step S706). Note that the terminal STA1-1 compatible with the IEEE802.11ax has already turned on the setting of its own OBSS_PD-based SRat the time of Step S702 and maintains this setting.

Note that this operation example 3 may add the following operations whenthe terminal STA1-1 compatible with the IEEE 802.11ax has received thePPDU frame or the like from the access point AP2. In Step S702, theterminal STA1-1 compatible with the IEEE 802.11ax turns on the settingof its own Two NAVs.

In Step S703, the terminal STA1-1 compatible with the IEEE 802.11axtransmits signaling which notifies the access point AP1 of the settingof its own Two NAVs.

In Step S705, the access point AP1 transmits signaling which instructsthe terminals to turn on the setting of the Two NAVs.

In Step S706, the terminal STA1-2 compatible with the IEEE 802.11axturns on the setting of its own Two NAVs.

Further, the following operations may be added instead of theaforementioned operations.

In Step S702, the terminal STA1-1 compatible with the IEEE 802.11axturns off the setting of its own Two NAVs.

In Step S703, the terminal STA1-1 compatible with the IEEE 802.11axtransmits signaling which notifies the access point AP1 of the settingof its own Two NAVs.

In Step S705, the access point AP1 transmits signaling which instructsthe terminals to turn off the setting of the Two NAVs.

In Step S706, the terminal STA1-2 compatible with the IEEE 802.11axturns off the setting of its own Two NAVs.

According to the third example embodiment, as described above, theaccess point AP and the terminal STA compatible with IEEE 802.11ax thatbelong to the BSS adaptively turn on/off the setting of theOBSS_PD-based SR.

This makes it possible to recognize a setting state of the OBSS_PD-basedSR in the access point AP and the terminal STA compatible with IEEE802.11ax, and thus makes it easier to predict a behavior of the entirewireless communication system.

Hereinafter, a configuration example of the access point AP and theterminal STA in a certain aspect, which has been described in theabove-described first to third example embodiments, is described.

FIG. 9 is a block diagram showing a configuration example of the accesspoint AP in a certain aspect. The access point AP includes acommunication unit 11, a processor 12, and a memory 13. Thecommunication unit 11 is configured to perform wireless communicationwith the terminals STA within the BSS to which it belongs and isconnected to the processor 12.

The memory 13 is configured to store an instruction set for performingprocessing of the access point AP described in the above-describedexample embodiments and software modules (computer programs) includingdata. The memory 13 may be composed of, for example, a combination of avolatile memory and a non-volatile memory.

The processor 12 is configured to read the software module (computerprogram) from the memory 13 and execute the software module to performprocessing of the access point AP described in the above embodiments.The processor 12 may be, for example, a microprocessor, a MicroProcessing Unit (MPU) or a Central Processing Unit (CPU). The processor12 may include a plurality of processors.

FIG. 10 is a block diagram showing a configuration example of theterminal STA in a certain aspect. The terminal STA includes acommunication unit 21, a processor 22, and a memory 23. Thecommunication unit 21 is configured to perform wireless communicationwith the access point AP within the BSS to which it belongs and isconnected to the processor 22.

The memory 23 is configured to store an instruction set for performingprocessing of the terminal STA described in the above-described exampleembodiments and software modules (computer programs) including data. Thememory 23 may be composed of, for example, a combination of a volatilememory and a non-volatile memory.

The processor 22 is configured to read the software module (computerprogram) from the memory 23 and execute the software module to performprocessing of the terminal STA described in the described exampleembodiments. The processor 22 may be, for example, a microprocessor, anMPU or a CPU. The processor 22 may include a plurality of processors.

The above-described program can be stored and provided to a computerusing any type of non-transitory computer readable media. Non-transitorycomputer readable media include any type of tangible storage media.Examples of non-transitory computer readable media include magneticstorage media (such as floppy disks, magnetic tapes, hard disk drives,etc.), optical magnetic storage media (e.g. magneto-optical disks),CD-ROM (compact disc read only memory), CD-R (compact disc recordable),CD-R/W (compact disc rewritable), and semiconductor memories (such asmask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM(random access memory), etc.). The program may be provided to a computerusing any type of transitory computer readable media. Examples oftransitory computer readable media include electric signals, opticalsignals, and electromagnetic waves. Transitory computer readable mediacan provide the program to a computer via a wired communication line(e.g. electric wires, and optical fibers) or a wireless communicationline.

Various aspects of the present invention have been described withreference to the example embodiments above. However, the presentinvention is not limited to the above. Various changes that can beunderstood by those skilled in the art can be made to the configurationand the details of each aspect of the present invention withoutdeparting from the scope of the invention. For example, the whole orpart of the above first, second and third example embodiments may bemutually combined and used.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2017-004666, filed on Jan. 13, 2017, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   AP ACCESS POINT-   STA TERMINAL-   11 COMMUNICATION UNIT-   12 PROCESSOR-   13 MEMORY-   21 COMMUNICATION UNIT-   22 PROCESSOR-   23 MEMORY

1. A wireless communication system comprising an access point (AP) thatbelongs to a Basic Service Set (BSS) and a terminal (STA) that belongsto the AP, wherein the STA updates a Network Allocation Vector (NAV)used for virtual carrier sense according to whether the AP and the STAare permitted to use Overlapping BSS (OBSS)_Power Detect (PD)-basedSpatial Reuse (SR) that includes a function of performing adjustment soas to avoid interference between the BSS and the OBSS.
 2. An accesspoint (AP) in a wireless communication system, the wirelesscommunication system comprising the AP that belongs to a Basic ServiceSet (BSS) and a terminal (STA) that belongs to the AP, the APcomprising: a memory configured to store instructions; and at least oneprocessor configured to process the instructions, wherein the processorinstructs the STA to update a Network Allocation Vector (NAV) used forvirtual carrier sense according to whether the AP and the STA arepermitted to use Overlapping BSS (OBSS)_Power Detect (PD)-based SpatialReuse (SR) that includes a function of performing adjustment so as toavoid interference between the BSS and the OBSS.
 3. A terminal (STA) ina wireless communication system, the wireless communication systemcomprising an access point (AP) that belongs to a Basic Service Set(BSS) and the STA that belongs to the AP, the STA comprising: a memoryconfigured to store instructions; and at least one processor configuredto process the instructions, wherein the processer updates a NetworkAllocation Vector (NAV) used for virtual carrier sense according towhether the AP and the STA are permitted to use Overlapping BSS(OBSS)_Power Detect (PD)-based Spatial Reuse (SR) that includes afunction of performing adjustment so as to avoid interference betweenthe BSS and the OBSS.
 4. The STA according to claim 3, wherein theprocessor does not update an Intra-BSS NAV and a Basic NAV based on anIntra-BSS frame received from the BSS and an Inter-BSS frame receivedfrom the OBSS when settings of the OBSS_PD-based SR in the AP and theSTA is set to on.
 5. The STA according to claim 3, wherein the processorupdates an Intra-BSS NAV and a Basic NAV based on an Intra-BSS framereceived from the BSS and an Inter-BSS frame received from the OBSS whenthe AP and the STA are not permitted to use the OBSS_PD-based SR.
 6. TheSTA according to claim 3, wherein when the AP and the STA are notpermitted to use the OBSS_PD-based SR, the processor performs thevirtual carrier sense by using an Intra-BSS NAV that is updated based ona NAV value included in an Intra-BSS frame received from the BSS and aBasic NAV that is updated based on a NAV value included in an Inter-BSSframe received form the OBSS.
 7. The STA according to claim 6, whereinwhen the AP and the STA are not permitted to use the OBSS_PD-based SR,the processor determines, upon receiving a frame, whether the receivedframe is the Intra-BSS frame or the Inter-BSS frame, wherein when theprocessor determines the received frame to be the Intra-BSS frame, theprocesser updates the Intra-BSS NAV based on a NAV value included in theIntra-BSS frame, and when the processor determines the received frame tobe the Inter-BSS frame, the processer updates the Basic NAV based on aNAV value included in the Inter-BSS frame.
 8. A communication methodperformed by an access point (AP) in a wireless communication system,the wireless communication system comprising the AP that belongs to aBasic Service Set (BSS) and a terminal (STA) that belongs to the AP, thecommunication method comprising instructing the STA to update a NetworkAllocation Vector (NAV) used for virtual carrier sense according towhether the AP and the STA are permitted to use Overlapping BSS(OBSS)_Power Detect (PD)-based Spatial Reuse (SR) that includes afunction of performing adjustment so as to avoid interference betweenthe BSS and the OBSS.
 9. A communication method performed by a terminal(STA) in a wireless communication system, the wireless communicationsystem comprising an access point (AP) that belongs to a Basic ServiceSet (BSS) and the STA that belongs to the AP, the communication methodcomprising updating a Network Allocation Vector (NAV) used for virtualcarrier sense according to whether the AP and the STA are permitted touse Overlapping BSS (OBSS)_Power Detect (PD)-based Spatial Reuse (SR)that includes a function of performing adjustment so as to avoidinterference between the BSS and the OBSS.